Project Summary According to the American Cancer Society, the 5-year overall survival rate of pancreatic cancer patients is approximately 9%. Gemcitabine is the standard therapy for pancreatic cancer, but it only increases patient survival by about 5 weeks. Despite breakthroughs in immune checkpoint inhibitors (ICI) immunotherapy in many types of human cancer. Pancreatic cancer stands out as one of the few human cancers that does not respond to ICI immunotherapy. New therapies therefore are in urgent need for pancreatic cancer. The underlying mechanism of pancreatic cancer non-response to ICI immunotherapy is currently unknown. One notion is that pancreatic cancer is a type of ?cold or nonimmunogenic? cancer that lacks cytotoxic T lymphocyte (CTL) tumor infiltration. We have recently shown that CTL infiltrates are present in the human pancreatic carcinoma and human pancreatic tumor cells express abundant PD-L1. Furthermore, literatures have shown that myeloid- derived suppressor cells (MDSCs) are abundant in the pancreatic cancer, and we and others have determined that MDSCs suppress CTLs through both PD-L1-dependent and PD-L1-independent mechanisms. It is therefore likely that CTLs are also suppressed by a PD-L1-independent mechanism that compensates for PD-L1 function in the pancreatic tumor microenvironment. We discovered in mouse tumor models and human cancer patients that osteopontin (OPN) acts as another immune checkpoint that negatively regulates T cell activation. Our published data and unpublished preliminary studies demonstrated strong scientific promise to target OPN to suppress pancreatic cancer immune evasion. Highly relevant to this proposal, we have developed a first-in-class OPN neutralization monoclonal antibody that is potent in reversing OPN-mediated suppression of T cell activation. Our central hypothesis is that OPN compensates for PD-L1 function in suppression of CTL activation and OPN mAb is effective in rendering pancreatic cancer response to ICI immunotherapy. To test this hypothesis, we will pursue the following two specific aims: 1) test the hypothesis that neutralizing OPN function increases the efficacy of anti-PD-1 immunotherapy in suppression of pancreatic cancer in vivo; and 2) humanize OPN mAb for human pancreatic cancer immunotherapy. Successful completion of the proposed studies has the potential to develop a humanized OPN monoclonal antibody for human pancreatic cancer immunotherapy.